The invention relates generally to the field of drilling and processing of wells, and particularly to techniques for sealing a liner within a casing during liner drilling.
Casing drilling and liner drilling have increasingly become important in the field of oil and gas exploration and production. In contrast to conventional drilling operations, casing and liner drilling involve creating and advancing a bore hole through horizons of possible interest by means of a bottom hole assembly, including a drill bit, attached to a casing or liner string. The casing and/or liner maintain the integrity of the bore hole, reduce the number of run-ins required to position and cement the casing and liner, and can more effectively and efficiently move from drilling to production.
Casing and liner drilling pose unique challenges due to the nature of the equipment and components used. For example, in conventional drilling operations, when a tubular member is to be sealed to a surrounding element, such as the borehole casing, a packer is typically employed. When used to seal (or pack off) a liner within a casing, for example, various packer designs may be employed that are actuated mechanically or hydraulically to force one or more packing elements to be forced into tight engagement between the tubing and the casing inner surface. In such operations, because a liner hanger used to hold the liner in place is itself a pressure containing vessel, a liner top packer may be used above the liner hanger.
In liner drilling, however, the liner hanger may not be desired to operate as a pressure vessel. The packer must therefore reside in the system below the hanger. Moreover, actuation of a conventional liner top packer is typically performed by setting a working tool string down on the packer to apply set-down weight to set the packer. However, with the packer integral to the liner string for liner drilling, this type of setting operation is not available.
There is a need, therefore, for novel arrangements and methods that allow for setting of a packer in a liner drilling tubular string. There is a particular need for a technique that may allow for setting a packer below a liner hanger, and that can be actuated internally to force a packing element into engagement between a liner string and a surrounding casing or liner.